The present invention pertains to a process for protecting a turbocompressor from operating in the unstable working range with a machine controller, which includes a surge limit controller and at least one of an intake pressure controller, an end pressure controller and a bypass controller, which performs an adjustment of a surge limit control valve and optionally of a said bypass valve, of an intake pressure control valve and of an actuating drive for compressor inlet vanes, which adjustment is controlled as a function of measured variables in the compressor inlet and the compressor outlet,.
An unstable state of a turbocompressor, in which gas being delivered flows jerkily or periodically back from the delivery side to the intake side, is called pumping. This unstable state appears at an excessively high end pressure and/or at an excessively low throughput. A line, which separates the stable range from the unstable range and is called the surge limit, can therefore be unambiguously defined in the characteristic diagram determined by the end pressure and the throughput or by coordinates derived therefrom. The working point of the turbocompressor is prevented by means of the surge limit controller from reaching the surge limit and pumping and the resulting pumping is thus prevented from developing. A control line is set for this purpose in the characteristic diagram at a safety distance from the surge limit. When the working point exceeds the control line, a relief valve (surge limit control valve) branching off from the compressor outlet is opened more or less widely in order to blow off medium being delivered or to blow it over to the intake side and to lower the end pressure and to increase the throughput as a result.
Control methods for avoiding the pumping of the compressor have been known according to which the position of the compressor working point in the characteristic diagram relative to the stability limit (surge limit) is determined by measuring variables in the inlet and outlet of the compressor (pressure, temperature, throughput) and control signals for adjusting surge limit control valves (blow-off or blow-by valves) are derived from this. The throughput through the turbocompressor as well as the pressure and the temperature at the inlet and the outlet of the turbocompressor are decisive for the operation of the turbocompressor. The measuring points are therefore always selected as close to the turbocompressor as possible.
The known prior art deals with measures whose goal is to recognize a shift of the working point in the direction of the surge limit early and to respond to it anticipatorily. Other measures have the goal of linearizing nonlinearities of the control circuit in order to obtain an optimal response behavior of the control system in all working ranges.
EP-PS 335 105 describes a process which [is intended to] detect a disturbance and to respond to same by measuring a process disturbance as close to the site at which it is generated as possible, i.e., as far away from the turbocompressor as possible. This patent assumes that a disturbance can be detected by measurement sooner at the site at which it is generated than at the turbocompressor proper and that a time lead is obtained as a result, which has a favorable effect on the control behavior. However, this patent also uses the measured data obtained close to the site at which the disturbance is generated only to treat them in exactly the same manner as the measured variables which are measured directly on the turbocompressor. The measured variables are used in a closed control circuit. However, this process has the drawback that it requires a deviation in order to bring about a change in the output variable.
The basic object of the present invention is to design the process of this type such that the unstable state of the turbocompressor can be detected and eliminated more reliably and rapidly.
According to the invention, a process is provided for protecting a turbocompressor with a downstream process from operation in the unstable working range. The process uses a machine controller, which optionally contains, besides a surge limit controller a intake pressure controller, an end pressure controller, a bypass controller, which performs an adjustment of a surge limit control valve and optionally of a bypass valve, of an intake pressure control valve and of an actuating drive for the compressor inlet vanes, which adjustment is controlled as a function of measured variables in the compressor inlet and the compressor outlet. A control matrix is determined from the position of a control unit (e.g., the fuel gas control valve), optionally taking into account additional influencing variables such as the compressor end pressure and the compressor outlet pressure and the compressor intake temperature as well as the process pressure. The control matrix is stored in the machine controller. The necessary position of the surge limit control valve as well as of the bypass valve, of the intake pressure control valve and of the actuating drive for the compressor inlet vanes is determined directly on the basis of this control matrix during a rapid transient change in the working point. This actuating variable is directly superimposed as a manipulated variable to the surge limit control valve, the intake pressure controller, the end pressure controller and the bypass controller.
The essential idea of the present invention is to calculate a variable from a measurement of the flow to the process as close to the process as possible, which variable corresponds to the future flow through the turbocompressor, and to derive from this measured variable a correction variable which directly actuates the surge limit control valve of the turbocompressor. It becomes possible in this manner to anticipatorily open the surge limit control valve before operation in the unstable working range for the protection of the turbocompressor.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which a preferred embodiment of the invention is illustrated.